U.S. patent application number 11/522490 was filed with the patent office on 2007-01-18 for method and apparatus for manufacturing an endovascular graft section.
This patent application is currently assigned to Boston Scientific Santa Rosa Corp.. Invention is credited to Michael V. Chobotov, Patrick Stephens.
Application Number | 20070012396 11/522490 |
Document ID | / |
Family ID | 21849637 |
Filed Date | 2007-01-18 |
United States Patent
Application |
20070012396 |
Kind Code |
A1 |
Chobotov; Michael V. ; et
al. |
January 18, 2007 |
Method and apparatus for manufacturing an endovascular graft
section
Abstract
A device and method for the manufacture of medical devices,
specifically, endovascular grafts, or sections thereof. Layers of
fusible material are disposed upon a shape forming member and seams
formed between the layers in a configuration that can produce
inflatable channels in desired portions of the graft. After
creation of the seams, the fusible material of the inflatable
channels may be fixed while the channels are in an expanded state.
A five axis robotic seam forming apparatus may be used to create
the seams in the layers of fusible material.
Inventors: |
Chobotov; Michael V.; (Santa
Rosa, CA) ; Stephens; Patrick; (Santa Rosa,
CA) |
Correspondence
Address: |
HOFFMANN & BARON, LLP
6900 JERICHO TURNPIKE
SYOSSET
NY
11791
US
|
Assignee: |
Boston Scientific Santa Rosa
Corp.
|
Family ID: |
21849637 |
Appl. No.: |
11/522490 |
Filed: |
September 15, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10029557 |
Dec 20, 2001 |
7125464 |
|
|
11522490 |
Sep 15, 2006 |
|
|
|
Current U.S.
Class: |
156/217 ;
156/190; 156/290 |
Current CPC
Class: |
B29C 66/43 20130101;
B29C 66/49 20130101; B29C 66/73713 20130101; B29C 66/9241 20130101;
B29L 2022/022 20130101; B29C 65/18 20130101; B29C 66/494 20130101;
B29C 66/65 20130101; B29C 66/71 20130101; B29L 2022/02 20130101;
A61F 2002/075 20130101; B29C 66/9261 20130101; B29C 66/71 20130101;
B29C 66/919 20130101; B29C 53/44 20130101; B29K 2027/18 20130101;
A61F 2230/0078 20130101; B29C 66/863 20130101; B29C 66/863
20130101; B29C 65/48 20130101; A61F 2250/0039 20130101; B29C
66/8161 20130101; A61F 2/07 20130101; B29C 66/8221 20130101; B29C
66/929 20130101; B29C 65/4815 20130101; B29C 53/42 20130101; B29C
66/4322 20130101; B29C 66/71 20130101; B29C 66/73712 20130101; B29C
66/8222 20130101; B29C 66/91445 20130101; B29C 66/91421 20130101;
A61F 2/89 20130101; B29C 66/12261 20130101; B29C 66/438 20130101;
B29C 66/91933 20130101; B29L 2031/7534 20130101; B29C 66/73711
20130101; Y10T 156/1002 20150115; B29C 66/71 20130101; B29C 66/1122
20130101; A61F 2250/0003 20130101; B29L 2031/7546 20130101; B29C
66/81422 20130101; Y10T 156/1036 20150115; B29C 66/836 20130101;
B29K 2067/00 20130101; B29K 2027/18 20130101; B29K 2023/0683
20130101; B29K 2023/0683 20130101; B29C 66/81812 20130101; B29C
65/00 20130101; B29C 66/91411 20130101 |
Class at
Publication: |
156/217 ;
156/190; 156/290 |
International
Class: |
B29C 53/00 20060101
B29C053/00 |
Claims
1-18. (canceled)
19. A method for manufacturing an endovascular graft, or section
thereof, comprising: a. disposing a first layer of fusible material
and at least one additional layer of fusible material onto a shape
forming member such that at least a portion of the first and second
layers is overlapped, forming an overlapped portion; b. selectively
fusing the layers of fusible material together in a seam to form at
least one inflatable channel in the overlapped portion of the first
and additional layers of fusible material wherein the shape forming
member comprises a cylindrical mandrel and wherein the first layer
and the at least one additional layer of fusible material are
disposed onto the mandrel by wrapping the layers thereabouts.
20. The method of claim 19 further comprising forming a plurality
of inflatable channels between the first and second layers of
fusible material.
21. The method of claim 20 wherein the plurality of channels are
all in fluid communication.
22. The method of claim 19 wherein the fusible material comprises
ePTFE.
23. The method of claim 19 wherein the inflatable channel is formed
between the first and additional layers of fusible material by the
application of heat and pressure.
24. The method of claim 24 wherein the application of heat and
pressure is carried out with a heated stylus that is pressed
against and translated relative to the overlapped portions.
25. The method of claim 24 wherein the movement of the heated
stylus relative to the overlapped portion is automatically
controlled.
26. The method of claim 25 wherein the movement of the heated
stylus relative to the overlapped portion may comprise up to five
axes of movement.
27. The method of claim 24 wherein the temperature of the heated
stylus tip is from about 350 to about 525 degrees Celsius.
28. The method of claim 24 wherein the pressure applied to the
layers in forming the seam is from about 300 to about 3,000
psi.
29. (canceled)
30. The method of claim 19 wherein the shape forming member
comprises a mandrel, wherein the first layer and the at least one
additional layer of fusible material are disposed onto the mandrel
by wrapping the layers thereabout, and wherein the mandrel
comprises a first end section, a second end section and a middle
section disposed between the first end section, the middle section
having transverse dimension less than a transverse dimension of the
first or second end sections.
31. The method of claim 19 wherein at least two seams are formed
between the at least two layers of fusible material to form at
least one inflatable channel disposed between layers of fusible
material.
32. The method of claim 31 wherein the inflatable channel is
expanded by internal pressure after being formed.
33. The method of claim 32 wherein a pressure line configured to
deliver fluid is inserted between the first and second layers of
fusible material.
34. The method of claim 33 wherein the pressure line comprises a
tubular member configured to be disposed between the first and
second layers of fusible material, the tubular member comprising a
plurality of apertures whose cross sections increase in size
distally along the tubular member.
35. The method of claim 32 further comprising sintering the
endovascular graft while the at least one inflatable channel is in
an expanded state.
36. The method of claim 35 wherein the at least one inflatable
channel is expanded into a mold while being sintered.
37-49. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 10/029,557, filed Dec. 20, 2001, the contents of which are
incorporated herein by reference.
RELATED TECHNOLOGY APPLICATIONS
[0002] This application is related to U.S. patent application Ser.
No. 10/029,570, filed Dec. 20, 2001, entitled "Method and Apparatus
for Shape Forming Endovascular Graft Material", by Chobotov, et
al., now U.S. Pat. No. 6,776,604; U.S. patent application Ser. No.
10/029,584, filed Dec. 20, 2001, entitled "Endovascular Graft Joint
and Method for Manufacture", by Chobotov et al., now U.S. Pat. No.
7,090,693; and U.S. patent application Ser. No. 10/029,559, filed
Dec. 20, 2001, entitled "Advanced Endovascular Graft", by Chobotov
et al. All of the above applications are commonly owned and were
filed on the same date. All of the above applications are hereby
incorporated by reference, each in their entirety.
BACKGROUND
[0003] Embodiments of the device and method discussed herein relate
to a system and method for manufacturing intracorporeal devices
used to replace, strengthen, or bypass body channels or lumens of
patients; in particular, those channels or lumens that have been
affected by conditions such as abdominal aortic aneurysms.
[0004] Existing methods of treating abdominal aortic aneurysms
include invasive surgical methods with grafts used to replace the
diseased portion of the artery. Although improvements in surgical
and anesthetic techniques have reduced perioperative and
postoperative morbidity and mortality, significant risks associated
with surgical repair (including myocardial infarction and other
complications related to coronary artery disease) still remain.
[0005] Due to the inherent hazards and complexities of such
surgical procedures, various attempts have been made to develop
alternative repair methods that involve the endovascular deployment
of grafts within aortic aneurysms. One such method is the
non-invasive technique of percutaneous delivery of grafts and
stent-grafts by a catheter-based system. Such a method is described
by Lawrence, Jr. et al. in "Percutaneous Endovascular Graft:
Experimental Evaluation", Radiology (1987). Lawrence et al.
describe therein the use of a Gianturco stent as disclosed in U.S.
Pat. No. 4,580,568 to Gianturco. The stent is used to position a
Dacron.RTM. fabric graft within the vessel. The Dacron.RTM. graft
is compressed within the catheter and then deployed within the
vessel to be treated.
[0006] A similar procedure is described by Mirich et al. in
"Percutaneously Placed Endovascular Grafts for Aortic Aneurysms:
Feasibility Study," Radiology (1989). Mirich et al. describe
therein a self-expanding metallic structure covered by a nylon
fabric, the structure being anchored by barbs at the proximal and
distal ends.
[0007] An improvement to percutaneously delivered grafts and
stent-grafts results from the use of materials such as expanded
polytetrafluoroethylene (ePTFE) for a graft body. This material,
and others like it, have clinically beneficial properties. However,
manufacturing a graft from ePTFE can be difficult and expensive.
For example, it is difficult to bond ePTFE with conventional
methods such as adhesives, etc. In addition, depending on the type
of ePTFE, the material can exhibit anisotropic behavior. Grafts are
generally deployed in arterial systems whose environments are
dynamic and which subject the devices to significant flexing and
changing fluid pressure flow. Stresses are generated that are
cyclic and potentially destructive to interface points of grafts,
particularly interface between soft and relatively hard or high
strength materials.
[0008] What has been needed is a method and device for
manufacturing intracorporeal devices used to replace, strengthen or
bypass body channels or lumens of a patient from ePTFE and similar
materials which is reliable, efficient and cost effective.
SUMMARY
[0009] Embodiments of the invention include a seam forming
apparatus configured to create one or more seams between overlapped
layers of fusible material of an endovascular graft section. The
apparatus includes a stylus and a mount system moveable relative to
the stylus in a controllable pattern. At least one motor is coupled
to the mount system and controllable by a preprogrammed database
that moves the mount system relative to the stylus in a
predetermined pattern. In some embodiments, the stylus may be
spring-loaded or actuated in a lateral direction, axial direction,
or both.
[0010] One particular embodiment of the seam forming apparatus
includes at least five motors controlled by a preprogrammed
database using automated techniques such as computer numerical
control (CNC) which are coupled to the mount system and configured
to move the mount system relative to the stylus in a different
degree of freedom for each motor. This embodiment, as well as the
embodiments described above, and others, allows the operator to
reliably form a section of an endovascular graft or other device in
an automated or semi-automated manner.
[0011] In use, the operator places the layers of fusible material
from which an endovascular graft will be formed onto the mount
system. The preprogrammed database then controls the movement of
the stylus tip so that a pattern of seams are formed in the layers
of fusible material to form the desired inflatable channels or any
other desirable configuration. As discussed above, such a system is
conducive to automation of the seam forming process and can
generate significant time and cost savings in the production of
endovascular grafts as well as other similar devices. Such a system
also generates accuracy and repeatability in the manufacture of
such medical devices.
[0012] In one embodiment of a method for forming a section of an
endovascular graft, or the like, a first layer of fusible material
is disposed onto a shape forming member or mandrel. A second layer
of fusible material is then disposed onto at least a portion of the
first layer forming an overlapped portion of the layers. A seam is
then formed in the layers of fusible material which is configured
to produce at least one inflatable channel in the overlapped
portion of the first and second layers of fusible material.
Thereafter, the inflatable channel can be expanded and the fusible
material which forms the channel fixed while the channel is in an
expanded state. In one embodiment, the fusible material is expanded
polytetrafluoroethylene (ePTFE) and the ePTFE material is fixed by
a sintering process. Materials such as fluorinated ethylene
propylene copolymer (FEP) and perfluoroalkoxy (PFA) can also be
disposed between the layers of fusible material prior to seam
formation; this can improve adhesion between the layers.
[0013] In another embodiment of a method for forming a section of
an endovascular graft, or the like, a first layer of fusible
material is disposed onto a shape forming member. At least one
expandable member, or portion thereof, is placed onto the first
layer of fusible material then an additional layer of fusible
material is disposed onto the first layer of fusible material and
at least a portion of the expandable member. A seam is formed
between the first and additional layers of fusible material
adjacent the expandable member securing the expandable member to
the layers of fusible material. The layers of fusible material can
then be selectively fused together in a seam forming at least one
inflatable channel in the overlapped portion of the first and
second layers of fusible material. The inflatable channel is then
expanded and the material forming the inflatable channel fixed when
the channel is in an expanded state.
[0014] In one embodiment, melt-processible materials can be
disposed on or adjacent the expandable member and first layer of
fusible material prior to placing the additional layer of fusible
material onto the first layer. Use of such a material (e.g., FEP,
PFA, etc.) can facilitate adhesion between the layers of fusible
material and serves a strain relief function for any dynamic
interaction between the expandable member and the endovascular
graft section made from the layers of fusible material. In some
embodiments, the expandable member can be a connector ring which is
configured to be secured to an expandable stent. The expandable
member can also be an expandable stent or the like.
[0015] These and other advantages of embodiments of the invention
will become more apparent from the following detailed description
of the invention when taken in conjunction with the accompanying
exemplary drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 illustrates a layer of fusible material being
positioned onto a shape forming mandrel.
[0017] FIG. 2 shows a first layer of fusible material disposed on a
shape forming 20 mandrel.
[0018] FIG. 2A is a transverse cross sectional view of the first
layer of fusible material and the shape forming mandrel of FIG. 2
taken along lines 2A-2A in FIG. 2.
[0019] FIG. 3 illustrates an additional layer of fusible material
being deposited onto 5 a shape forming mandrel.
[0020] FIG. 4 shows the first layer of fusible material being
trimmed by an instrument.
[0021] FIG. 5 is a transverse cross sectional view of the layers of
fusible material and shape forming mandrel of FIG. 5 taken along
lines 5-5 of FIG. 4.
[0022] FIG. 6 illustrates additional layers of fusible material
being deposited on the shape forming mandrel.
[0023] FIG. 7 illustrates an inflation line being positioned on the
first and additional layers of fusible material of FIG. 6.
[0024] FIGS. 7A and 7B illustrate the formation of the inflation
line of FIG. 7.
[0025] FIG. 8 shows two expandable members positioned on the layers
of fusible material of FIG. 7.
[0026] FIG. 9 illustrates the deposition of an adhesive or melt
processible material adjacent a connector member of the graft body
section under construction.
[0027] FIG. 10 shows another additional layer of fusible material
being deposited 20 onto the graft body section.
[0028] FIG. 11 illustrates excess fusible material being trimmed
from the first end and second end of the graft body section
adjacent the connector members.
[0029] FIG. 12 is an elevational view of the graft body section
with the fusible material trimmed away and removed.
[0030] FIG. 13A is a side view from the right hand side of a five
axis seam forming apparatus.
[0031] FIG. 13B is a side view from the left hand side of a five
axis seam forming apparatus.
[0032] FIG. 13C is a front view of the five axis seam forming
apparatus of FIGS. 13A and 13B.
[0033] FIG. 13D shows a stylus tip in contact with a transverse
cross sectioned view of a cylindrical shape forming member with an
axis of the stylus tip oriented at an angle with the tangent of the
shape forming member at the point of contact therebetween.
[0034] FIG. 13E illustrates a stylus tip in contact with a
plurality of layers of fusible material in a substantially flat
configuration with the longitudinal axis of the stylus tip at an
angle with respect to a line which is orthogonal to the surface of
the layers.
[0035] FIG. 13F is a front view of the seam forming apparatus with
a shape forming mandrel and a graft body section on the shape
forming mandrel positioned in the chuck of the seam forming member
mount system.
[0036] FIG. 13G illustrates a distal extremity or tip of a stylus
in contact with the layers of fusible material of the graft body
section.
[0037] FIG. 13H illustrates the tip of a stylus in contact with
layers of fusible material of the graft body section, forming a
seam in the layers.
[0038] FIG. 14 shows inflation channels being formed in the layers
of fusible material on the shape forming mandrel by the seam
forming apparatus stylus tip.
[0039] FIG. 15 shows the graft body section with the channel
formation complete and pressurized fluid being injected into an
inflatable channel network in order to expand the inflatable
channels.
[0040] FIG. 16A illustrates one half of an embodiment of a
two-piece mold for use during expansion of the inflatable channels
formed by the seam forming 10 apparatus.
[0041] FIG. 16B is an end view showing the shape forming mandrel
and graft body section within both halves of the mold.
[0042] FIG. 16C shows the graft body section and shape forming
mandrel disposed within the mold cavity (with one half of the mold
removed for clarity of illustration) with a fluid being injected
into the inflatable channels of the graft body section in order to
keep the inflatable channels in an expanded state during the fixing
or sintering of the fusible material.
[0043] FIG. 17 illustrates an outer layer or layers of fusible
material being forced into the mold cavity of a portion of the mold
by pressurized fluid as indicated by the dotted line.
[0044] FIG. 18 is an elevational view in partial section of an
embodiment of an inflatable endovascular graft of the present
invention.
[0045] FIG. 19 is an enlarged view of the graft of FIG. 18 taken at
the dashed circle indicated by numeral 19 in FIG. 18.
[0046] FIG. 20 is an enlarged view in section taken along lines
20-20 in FIG. 18.
[0047] FIG. 21 is a transverse cross sectional view of the graft of
FIG. 18 taken along lines 21-21 in FIG. 18.
[0048] FIG. 22 is a transverse cross sectional view of the graft of
FIG. 18 taken along lines 22-22 in FIG. 18.
[0049] FIG. 23 is a transverse cross sectional view of the graft of
FIG. 18 taken along lines 23-23 in FIG. 18.
DETAILED DESCRIPTION
[0050] FIG. 1 illustrates a sheet of fusible material 10 stored on
an elongate drum 11. The drum 11 is rotatable, substantially
circular in transverse cross section and has a transverse dimension
in the longitudinal center 12 that is greater than the transverse
dimension of either end of the drum. The sheet of fusible material
10 is being rolled from the elongate drum in a single layer 13 onto
an interior surface support means in the form of a cylindrical or
tapered (conical) shape forming member or mandrel 14 to form a body
section 15 of an endovascular graft 16. The body section 15 has a
proximal end 17 and a distal end 18. For the purposes of this
application, with reference to endovascular graft devices, the
proximal end 17 describes the end of the graft that will be
oriented towards the oncoming flow of bodily fluid, usually blood,
when the device is deployed within a conduit of a patient's body.
The distal end 18 of the graft is the end opposite the proximal
end.
[0051] A single layer of fusible material 13 is a term that
generally refers to a sheet of material that is not easily
separated by mechanical manipulation into additional layers. The
shape forming mandrel 14 is substantially cylindrical in
configuration, although other configurations are possible. Middle
section 20 of mandrel 14 shown in FIGS. 1-2 has a transverse
dimension which is smaller than the transverse dimension of a first
end section 21 and a second end section 22. The shape forming
mandrel may have a first tapered section 23 at the first end and a
second tapered section 24 at the second end. The sheet of fusible
material 10 is shown being rolled off the elongate drum 11 in the
direction indicated by the arrow 11A with the lead end 25 of the
first layer of fusible material 10 oriented longitudinally along an
outside surface 14A of the shape forming mandrel 14.
[0052] The fusible material in the embodiment illustrated in FIG. 1
is ePTFE that ranges from about 0.0005 to about 0.010 inch in
thickness; specifically from about 0.001 to about 0.003 inch in
thickness. The sheet being disposed or rolled onto the shape
forming mandrel 14 may range from about 2 to about 10 inches in
width; specifically, from about 3 to about 7 inches in width,
depending on the indication and size of the end product.
[0053] The ePTFE material sheet 10 in FIG. 1 is a fluoropolymer
with a node and fibril composition with the fibrils oriented in
primarily a uniaxial direction substantially aligned with the
longitudinal axis of shape forming mandrel 14. Other nodal/fibril
orientations of ePTFE could also be used for this layer, including
multiaxially oriented fibril configurations or uniaxial material
oriented substantially circumferentially about shape forming
mandrel 14 or at any desired angle between substantial alignment
with the longitudinal axis and substantial alignment with a
circumferential line about the shape forming mandrel 14. Uniaxially
oriented ePTFE materials tend to have greater tensile strength
along the direction of fibril orientation, so fibril orientation
can be chosen to accommodate the greatest stresses imposed upon the
finished product for the particular layer, combination of layers,
and portion of the product where such stress accommodation is
needed.
[0054] The layers of fusible material made of ePTFE are generally
applied or wrapped in an unsintered state. By applying the ePTFE
layers in an unsintered or partially sintered state, the graft body
section 15, upon completion, can then be sintered or fixed as a
whole in order to form a cohesive monolithic structure with all
contacting surfaces of ePTFE layers achieving some level of
interlayer adhesion. It may, however, be desirable to apply some
layers of fusible material that have been pre-sintered or pre-fixed
in order to achieve a desired result or to assist in the handling
of the materials during the construction process. For example, it
may be desirable in some embodiments to sinter the single layer 13
of fusible material applied to the shape forming mandrel 14 in
order to act as a better insulator between the shape forming
mandrel 14, which can act as a significant heat sink, and
subsequent layers of fusible material which may be welded by seam
formation in some locations in order to, create inflatable
channels.
[0055] The amount of expansion of the ePTFE material used for the
construction of endovascular grafts and other devices can vary
significantly depending on the desired characteristics of the
material and the finished product. Typically, the ePTFE materials
processed by the devices and methods discussed herein may have a
density ranging from about 0.4 to about 2 grams/cc; specifically,
from about 0.5 to about 0.9 grams/cc. The nodal spacing of the
uniaxial ePTFE material may range from about 0.5 to about 200
microns; specifically, from about 5 to about 35 microns. The nodal
spacing for multiaxial ePTFE material may range from about 0.5 to
about 20 microns; specifically, from about 1 to about 2
microns.
[0056] Although FIG. 1 illustrates a layer of fusible material that
is made of ePTFE, the methods described herein are also suitable
for a variety of other fusible materials. Examples of other
suitable fusible materials for endovascular graft construction and
other applications include PTFE, porous PTFE, ultra high molecular
weight polyethylene, polyesters, and the like.
[0057] FIGS. 2 and 2A depict a first layer of fusible material 26
disposed on the shape forming mandrel 14 with an overlapped portion
27 of the first layer 26 on itself. A terminal end 28 of the first
layer 26 is seen extending longitudinally along the length of the
shape forming mandrel 14. As the layer of fusible material is
wrapped onto shape forming mandrel 14, some tension may be provided
on the sheet of material by the elongate drum 11. As a result of
this tension and the flexible and conforming properties of the
ePTFE material, the first layer of material 26 conforms closely to
the outer contour of the shape forming mandrel 14 as is illustrated
in FIG. 2.
[0058] In some embodiments, it may be desirable to pass the tip of
a seam forming tool or similar device (not shown) along the
overlapped portion 27 of first layer 26 in a longitudinal direction
in order to form a seam (not shown) along the overlapped portion 27
of first layer 26. A tool suitable for forming such a longitudinal
seam is a soldering iron with a smooth, rounded tip that will not
catch or tear the layer of fusible material. An appropriate
operating temperature for the tip of such a tool may range from
about 320 to about 550 degrees Celsius; specifically, from about
380 to about 420 degrees Celsius.
[0059] FIG. 3 illustrates an additional layer of fusible material
30 being disposed or wrapped onto the first layer of fusible
material 26 in a manner similar to that described above for the
first layer 26. Both uniaxial and multiaxial ePTFE may be used for
this additional layer 30. A lead end 31 of the additional layer can
be seen adjacent the terminal end 28 of the first layer 26. Tension
on the additional layer of fusible material 30 helps to make the
additional layer 30 conform to the shape forming mandrel 14 as seen
in the illustration. Although a single additional layer 30 is shown
in FIG. 3 as being disposed onto the first layer 26, it is within
the scope of the invention to wrap multiple additional layers 30 of
fusible material in this step. We have found that wrapping two
additional layers 30 of multiaxial ePTFE onto the first layer 26
helps to form a useful graft body section 15.
[0060] FIG. 4 shows an optional step in which the first and
additional layers of fusible material 26 and 30 which form the
graft body section 15 under construction are trimmed by knife edge
32 or a similar tool which is pressed against the layers of
material and moved circumferentially about the shape forming
mandrel 14. FIG. 5 is a transverse cross sectional view of the
shape forming mandrel 14 and graft body section 15 of FIG. 5 taken
along lines 5-5 in FIG. 4. The overlapped portion 27 of the first
layer 26 and an overlapped portion 33 of the additional layer 30 of
fusible material can be seen. It may be desirable to create a
longitudinal seam in the overlapped portion 33 of the additional
layer 30 in a manner similar to that of the first layer 26
discussed above using the same or similar tools.
[0061] FIG. 6 illustrates a proximal end wrap 34 of fusible
material being applied to the additional layer 30 of graft body
section 15, preferably under some tension. We have found it useful
to have end wrap 34 be uniaxial ePTFE, with the fibrils of the end
wrap material oriented circumferentially about the shape forming
mandrel 14, although other orientations and types of ePTFE are
possible. The end wrap material may have a thickness ranging from
about 0.0005 to about 0.005 inch; specifically, from about 0.001 to
about 0.002 inch. The width of the end wrap material may range from
about 0.25 to about 2.0 inch; specifically, from about 0.5 to about
1.0 inch. One or more layers of end wrap 34 (in any desired
orientation) may be built up onto the proximal end 17 of graft body
section 15 on shape forming mandrel 14. The additional end wrap
layer or layers 34 may be applied in a manner similar to that of
the first layer 26 and additional layers 30 as discussed above.
[0062] FIG. 7 shows graft body section 15 with the end wrap layer
34 completed with an inflation line 36 disposed on or near the
distal end 18 of graft body section 15. The inflation line 36 may
be constructed as shown in FIGS. 7A and 7B of ePTFE by wrapping one
or more layers of the material about a cylindrical mandrel 37. A
longitudinal seam 38 can then be formed in an overlapped portion of
the layers by passing the tip of a seam forming tool 39 along the
overlapped portion of the first layer in a longitudinal direction
in order to form a seam 38 along the overlapped portion of the
layers of the inflation line 36. A tool suitable for forming such a
longitudinal seam is a soldering iron with a smooth rounded tip
that will not catch or tear the layer of fusible material;
operating temperatures for the tip may range as previously
discussed. Alternatively, the inflation line 36 may be formed using
an ePTFE extrusion placed over a mandrel.
[0063] Once seam 38 is formed in inflation line 36, the fusible
material of inflation line 36 may can be fixed or sintered by
heating to a predetermined temperature for a predetermined time.
For embodiments of the inflation line 36 made of ePTFE, the layers
are sintered by bringing the layered assembly to a temperature
ranging from about 335 to about 380 degrees Celsius (for unsintered
material) and about 320 to about 380 degrees Celsius (for sintering
material that was previously sintered) and then cooling the
assembly to a temperature ranging from about 180 to about 220
degrees Celsius. The inflation line 36 may then be removed from
mandrel 37 and disposed on a graft body assembly 40 as shown in
FIG. 7. The inflation line 36 may be pre-fixed or pre-sintered to
avoid having the inner surfaces of the inflation line 36 stick
together during the construction and processing of the graft and
possibly block the inflation line 36.
[0064] In FIG. 8, expandable members in the form of a proximal
connector member 41 and a distal connector member 42 have been
disposed onto the graft body section 15 towards the respective
graft body section proximal end 17 and distal end 18. The proximal
connector member 41 is an elongate flexible metal element
configured as a ring, with the ring having a zig-zag or serpentine
pattern around the circumference of the ring. The distal connector
member 42 can have a similar configuration; note the feature of
this element in which an extended apex 44 is disposed over
inflation line 36 to further stabilize graft section 15. This
configuration allows the connector members 41 and 42 to be radially
constrained and radially expanded while maintaining a circular ring
configuration. The embodiment of the connector members 41 and 42
shown in FIG. 8 may be constructed of any suitable biocompatible
material; most suitable are metals, alloys, polymers and their
composites known to have superelastic properties that allow for
high levels of strain without plastic deformation, such as nickel
titanium (NiTi). Other alloys such as stainless steel may also be
used. Connector members 41 and 42 shown are also configured to be
self-expanding from a radially constrained state. The serpentine
pattern of the connector members 41 and 42 is disposed over base
layers of the graft body section as are connector elements 43 which
are disposed on certain apices 44 of the serpentine pattern of the
connector members 41 and 42. The embodiments of the connector
members 41 and 42 shown in FIG. 8 have been shape formed to lie
substantially flat against the contour of the outer surface of the
shape forming mandrel 14. Although the embodiment of FIG. 8
illustrates connector members 41 and 42 being disposed upon the
graft body section 15, expandable members including stents or the
like may be used in place of the connector members 41 and 42.
[0065] An optional adhesive or melt-processible material such as
FEP or PFA may be deposited adjacent the connector members 41 and
42 prior to the addition of additional layers of fusible material
to the graft body section 15, as is shown in FIG. 9. Materials such
as FEP or PFA can help the layers of fusible material to adhere to
the connector members 41 and 42, to inflation line 36 (in the case
of distal member 42), and to each other. In addition, such material
may serve to provide strain relief between connector members 41 and
42 and the adhered or bonded layers of fusible material (and
inflation line 36) adjacent the wire of the connector members 41
and 42. It has been determined that one of the areas of greatest
concentrated stress within an endovascular structure such as that
described herein, when deployed within a dynamic biological system,
such as an artery of a human patient, is at the junction between
the connector members 41 and 42 and graft body section 15.
Therefore, it may be desirable to include materials such as FEP or
PFA or some other form of strength enhancement or strain relief in
the vicinity of this junction.
[0066] An outer overall wrap layer 50 may thereafter be applied to
the graft body section 15 and connector members 41 and 42 as shown
in FIG. 10. The outer overall wrap layer 50 can include one, two,
three or more layers of multiaxial ePTFE, usually about 2 to about
4 layers, but uniaxial ePTFE other suitable fusible materials,
fibril orientation and layer numbers could also be used. The outer
overall wrap layer 50 is most usefully applied under some tension
in order for the layer or layers to best conform to the outer
contour of the shape forming mandrel 14 and graft body section 15.
When the outer layer 50 comprises multiaxial ePTFE, there is
generally no substantially preferred orientation of nodes and
fibrils within the microstructure of the material. This result in a
generally isotropic material whose mechanical properties, such as
tensile strength, are generally comparable in all directions (as
opposed to significantly different properties in different
directions for uniaxially expanded ePTFE). The density and
thickness of the multiaxial material can be the same as or similar
to those dimensions discussed above.
[0067] Although not shown in the figures, we have found it useful
to add one or more optional cuff-reinforcing layers prior to the
addition of an overall wrap layer 50 as discussed below in
conjunction with FIG. 10. Typically this cuff-reinforcing layer is
circumferentially applied to graft body section 15 at or near the
graft body section proximal end 17 so to provide additional
strength to the graft body section proximal end 17 in those designs
in which a proximal cuff (and possibly a proximal rib) are used.
Typically the graft experiences larger strains during fabrication
and in service in the region of the proximal cuff, especially if a
larger cuff is present. This optional cuff-reinforcing layer
typically is multiaxial ePTFE, although uniaxial ePTFE and other
materials may be used as well. We have found effective a
cuff-reinforcing layer width from about 20 to about 100 mm;
specifically, about 70 mm. Functionally, however, any width
sufficient to reinforce the proximal end of graft body section 15
may be used.
[0068] Once the additional layer or layers of fusible material and
additional graft elements such as the connector members 41 and 42
and inflation line 36 have been applied, any excess fusible
material may be trimmed away from the proximal end 17 and distal
end 18 of graft body section 15. FIG. 11 illustrates one or more
layers of fusible material being trimmed from the proximal end 17
and distal end 18 of the graft body section 15 so as to leave the
connector members 41 and 42 embedded between layers of fusible
material but with the connector elements 43 exposed and a distal
end 51 of the inflation line 36 exposed as shown in FIG. 12. Once
the fusible material has been trimmed from the proximal end 17 and
the distal end 18, as discussed above, an additional process may
optionally be performed on the proximal end 17, distal end 18 or
both the proximal end and distal end 17 and 18. In this optional
process (not shown in the figures), the outer wrap 50 is removed
from a portion of the connector members 41 and 42 so as to expose a
portion of the connector members 41 and 42 and the additional layer
of fusible material 30 beneath the connector member 42 and the
proximal end wrap 34 beneath connector member 41. Once exposed, one
or more layers of the additional layer or layers 30 or proximal end
wrap 34 may have cuts made therein to form flaps which can be
folded back over the respective connector members 42 and 41 and
secured to form a joint (not shown). One or more layers of fusible
material can then be disposed over such a joint to provide
additional strength and cover up the joint. The construction of
such a joint is discussed in U.S. Pat. No. 7,090,693, entitled
"Endovascular Graft Joint and Method for Manufacture" by Chobotov
et al. which has been incorporated by reference herein.
[0069] Once the graft body section 15 has been trimmed, the entire
shape forming mandrel 14 and graft body section 15 assembly is
moved to a seam forming apparatus 52 illustrated in FIGS. 13A-13H.
This seam forming apparatus 52 has a base 53 and a vertical support
platform 54 which extends vertically upward from the back edge of
the base 53. A mount system 55 is secured to the base 53 and for
the embodiment shown in the figures, consists of a motor drive
chuck unit 56 secured to a riser 57 and a live center unit 58
secured to a riser 59. Both risers 57 and 59 are secured to the
base 53 as shown. The axis of rotation 55A of the chuck 60 of the
motor drive chuck unit 56 and the axis of rotation 55B of the live
center 61 of the live center unit 58 are aligned or concentric as
indicated by dashed line 55C. A motor is mechanically coupled to
the chuck 60 of the motor drive chuck unit 56 and serves to rotate
the chuck 60 in a controllable manner.
[0070] A vertical translation rack 62 is secured to the vertical
support platform 54 and extends from the base 53 to the top of the
vertical support platform 54. A vertical car 63 is slidingly
engaged on the vertical translation rack 62 and can be moved along
the vertical translation rack 62, as shown by arrows 63A, in a
controllable manner by a motor and pinion assembly (not shown)
secured to the vertical car 63. A horizontal translation rack 64 is
secured to the vertical car 63 and extends from the left side of
the vertical car 63 to the right side of the vertical car 63. A
horizontal car 65 is slidingly engaged on the horizontal
translation rack 64 and can be moved along the horizontal rack 64,
as shown by arrow 64A, in a controllable manner by a motor and
pinion assembly (not shown) which is secured to the horizontal car
65.
[0071] A stylus rotation unit 66 is slidingly engaged with a second
horizontal translation rack 65A disposed on the horizontal car 65
and can be moved towards and away from the vertical car 63 and
vertical support platform 54 in a controllable manner as shown by
arrow 66A. A stylus rotation shaft 67 extends vertically downward
from the stylus rotation unit 66 and rotates about an axis as
indicated by dashed line 67B and arrow 67A in a controllable
manner. A stylus mount 68 is secured to the bottom end of the
rotation shaft 67 and has a main body portion 69 and a stylus pivot
shaft 70. A stylus housing 71 is rotatably secured to the stylus
mount 68 by the stylus pivot shaft 70. A torsion spring 72 is
disposed between the proximal end of the stylus housing 73 and the
stylus mount 68 and applies a predetermined amount of compressive,
or spring-loaded force to the proximal end 73 of the stylus housing
71. This in turn determines the amount of tip pressure applied by a
distal extremity 80 of a stylus tip 75 disposed at the distal end
section 78 of the stylus 79 (which is in turn secured to the distal
end section 76 of the stylus housing 71).
[0072] The base 53 of seam forming apparatus 52 is secured to a
control unit housing 77 which contains one or more power supplies,
a CPU, and a memory storage unit that are used in an automated
fashion to control movement between the graft body 15 section and
the stylus tip 75 in the various degrees of freedom therebetween.
The embodiment of the seam forming apparatus 52 described above has
five axes of movement (or degrees of freedom) between an object
secured to the chuck 60 and live center 61 and the stylus tip 75;
however, it is possible to have additional axes of movement, such
as six, seven, or more. Also, for some configurations and seam
forming processes, it may be possible to use fewer axes of
movement, such as two, three, or four. In addition, any number of
configurations may be used to achieve the desired number of degrees
of freedom between the stylus 79 and the mounted device. For
example, additional axes of translation or rotation could be added
to the mount system and taken away from the stylus rotation unit
66. Although the embodiment of the shape forming mandrel 14 shown
in FIGS. 1-17 is cylindrical, a five axis or six axis seam forming
apparatus has the capability and versatility to accurately create
seams of most any desired configuration on a shape forming member
or mandrel of a wide variety of shapes and sizes. For example, a
"Y" shaped mandrel suitable for generating a bifurcated graft body
section could be navigated by the five axis seam forming apparatus
illustrated herein, as well as other shapes. Finally, seam forming
apparatus 52 illustrated herein is but one of a number of devices
and configurations capable of achieving the seams of the present
inventions
[0073] FIG. 13D illustrates an enlarged view of a stylus tip 75
applied to a rotating cylindrical surface 86B with the surface
rotating in a counterclockwise direction as indicated by arrow 86A.
The cylindrical surface can support one or more layers of fusible
material (not shown) between the distal extremity 80 of the stylus
tip 75 and the surface 86B which require seam to be formed therein.
The stylus tip 75 has a longitudinal axis that forms an angle 86
with a tangent to the surface of the cylindrical surface indicated
by dashed line 87. Although not necessary, we have found it useful
to have the object in contact with the stylus tip 75 rotating or
moving in a direction as show in FIG. 13D, relative to angle 86 in
order to prevent chatter of the configuration or distortion of
fusible material on the surface 86A. In one embodiment, angle 86
may range from about 5 to about 60 degrees; specifically, from
about 10 to about 20 degrees. It is also useful if the distal
extremity 80 of the stylus tip 75 has a smooth surface and is
radiused. A suitable radius for one embodiment may range from about
0.01 to about 0.030 inch; specifically, from about 0.015 to about
0.02 inch.
[0074] FIG. 13E shows a similar relationship between a stylus tip
75 and hard surface 81. Surface 81 may have one or more layers of
fusible material (not shown) disposed thereon between distal
extremity 80 and surface 81. A longitudinal axis 75A of stylus tip
75 forms an angle 86 with the dashed line 89 that is parallel to
surface 81. Angle 88 in this embodiment should range from about 5
to about 60 degrees; specifically, from about 10 to about 20
degrees, so to ensure smooth relative motion between surface 81 and
tip 75. The surface 81 is shown moving relative to the stylus tip
75 in the direction indicated by arrow 81A.
[0075] The pressure exerted by the extremity 80 of stylus tip 75 on
the material being processed is another parameter that can affect
the quality of a seam formed in layers of fusible material. In one
embodiment in which the stylus tip is heated, the pressure exerted
by the distal extremity 80 of the stylus tip 75 may range from
about 100 to about 6,000 pounds per square inch (psi);
specifically, from about 300 to about 3,000 psi. The speed of the
heated stylus 75 relative to the material being processed, such as
that of graft body section 15, may range from about 0.2 to about 10
mm per second, specifically, from about 0.5 to about 1.5 mm per
second. The temperature of the distal extremity 80 of the heated
stylus tip 75 in this embodiment may range from about 320 to about
550 degrees Celsius; specifically, about 380 to about 420 degrees
Celsius.
[0076] Seam formation for ePTFE normally occurs by virtue of the
application of both heat and pressure. The temperatures at the tip
of the heated stylus 75 during such seam formation are generally
above the melting point of highly crystalline ePTFE, which may
range be from about 327 to about 340 degrees Celsius, depending in
part on whether the material is virgin material or has previously
been sintered). In one embodiment, the stylus tip temperature for
ePTFE welding and seam formation is about 400 degrees Celsius.
Pressing such a heated tip 75 into the layers of ePTFE against a
hard surface such as the outside surface of the shape forming
mandrel) compacts and heats the adjacent layers to form a seam with
adhesion between at least two of, if not all, the layers. At the
seam location and perhaps some distance away from the seam, the
ePTFE generally transforms from an expanded state with a low
specific gravity to a non-expanded state (i.e., PTFE) with a
relatively high specific gravity. Some meshing and entanglement of
nodes and fibrils of adjacent layers of ePTFE may occur and add to
the strength of the seam formed by thermal-compaction. The overall
result of a well-formed seam between two or more layers of ePTFE is
adhesion that can be nearly as strong or as strong as the material
adjacent the seam. The microstructure of the layers may change in
the seam vicinity such that the seam will be impervious to fluid
penetration.
[0077] It is important to note that a large number of parameters
determine the proper conditions for creating the fusible material
seam, especially when that material is ePTFE. Such parameters
include, but are not limited to, the time the stylus tip 75 is in
contact with the material (or for continuous seams, the rate of tip
movement), the temperature (of the tip extremity 80 as well as that
of the material, the underlying surface 81, and the room), tip
contact pressure, the heat capacity of the material, the mandrel,
and the other equipment, the characteristics of the material (e.g.
the node and fibril spacing, etc.), the number of material layers
present, the contact angle between the tip extremity 80 and the
material, the shape of the extremity 80, etc. Knowledge of these
various parameters is useful in determining the optimal combination
of controllable parameters in forming the optimal seam. And
although typically a combination of heat and pressure is useful in
forming an ePTFE seam, under proper conditions a useful seam may be
formed by pressure at ambient temperature (followed by elevation to
sintering temperature); likewise, a useful seam may also be formed
by elevated temperature and little-to-no applied pressure.
[0078] For example, we have created seams in ePTFE that formed an
intact, inflatable cuff by the use of a clamshell mold that
presented an interference fit on either side of a cuff zone for the
ePTFE. The application of pressure alone without using an elevated
temperature prior to sintering formed a seam sufficient to create a
working cuff.
[0079] FIG. 13F depicts a front view of the seam forming apparatus
52 with a shape forming mandrel 14 secured to the chuck 60 and the
live center unit 58. The distal extremity of the heated stylus tip
75 is in contact with the graft body section 15 which is disposed
on the shape forming mandrel 14. The chuck 60 is turning the shape
forming mandrel 14 and graft body section 15 in the direction
indicated by the arrow 60A to form a seam 81 between the layers of
fusible material of the graft body section 15.
[0080] FIGS. 13G and 13H illustrate an enlarged view of the heated
stylus tip 75 in contact with the graft body section 15 in the
process of creating one ore more seams 81 which are configured to
form elongate inflatable channels 82 in the graft body section 15.
The term "inflatable channels" may generally be described herein as
a substantially enclosed or enclosed volume between layers of
fusible material on a graft or graft section, and in some
embodiments, in fluid communication with at least one inlet port
for injection of inflation material. The enclosed volume of an
inflatable channel or cuff may be zero if the inflatable cuff or
channel is collapsed in a non-expanded state. The enclosed volume
of an inflatable channel may or may not be collapsible during
compression or compacting of the graft body section 15.
[0081] FIG. 13H is an enlarged view in section of the distal
extremity 80 of the heated stylus tip 75 in contact with layers of
fusible material of graft body section 15. The layers of fusible
material are being heated and compressed to form a bond 15A
therebetween. The seam forming apparatus can position the distal
extremity 80 at any desired location on the graft body section 15
by activation of one or more of the five motors controlled by the
components in the control unit housing 77. Each of the five motors
controls relative movement between graft body section 15 and distal
extremity 80 in one degree of freedom. Thus, the distal extremity
80 may be positioned above the surface of the graft body section
15, as shown in FIG. 13C, and brought to an appropriate temperature
for seam formation, as discussed above, by resistive heating or any
other appropriate method. Once extremity 80 has reached the target
temperature, it can be lowered by activation of the motor which
controls movement of the vertical car. The extremity 80 can be
lowered and horizontally positioned by other control motors until
it contacts the graft body section in a desired predetermined
position on graft body section 15, as shown in FIG. 13F.
[0082] Once distal extremity 80 makes contact with graft body
section 15 with the proper amount of pressure, it begins to form a
seam between the layers of the fusible material of the graft body
section as shown in FIG. 13H. The pressure or force exerted by the
extremity 80 on the graft body section may be determined by the
spring constant and amount of deflection of torsion spring 72 shown
in FIGS. 13A and 13B; generally, we have found a force at the
extremity 80 ranging from about 0.2 to about 100 grams to be
useful. As the seam formation process continues, the surface of
graft body section 15 may be translated with respect to the distal
extremity 80 while desirably maintaining a fixed, predetermined
amount of pressure between the distal extremity 80 and the layers
of fusible material of the graft body section. The CPU (or an
equivalent device capable of controlling the components of
apparatus 52) of the control unit housing 77 may be programmed, for
instance, a mathematical representation of the outer surface
contour of any known shape forming member or mandrel.
[0083] The CPU is thereby able to control movement of the five
motors of apparatus 52, so that distal extremity 80 may follow the
contour of the shape forming member while desirably exerting a
fixed predetermined amount of pressure the layers of fusible
material disposed between the distal extremity 80 and the shape
forming member. While seam formation is taking place, the pressure
exerted by the distal extremity 80 on the shape forming member may
be adjusted dynamically. The extremity 80 may also be lifted off
the graft body section and shape forming member in locations where
there is a break in the desired seam pattern. Once distal extremity
80 is positioned above the location of the starting point of the
next seam following the break, the extremity 80 may then be lowered
to contact the layers of fusible material, reinitiating the seam
formation process.
[0084] Use of the seam forming apparatus 52 as described herein is
but one of a number of ways to create the desired seams in the
graft body section 15 of the present invention. Any suitable
process and apparatus may be used as necessary and the invention is
not so limited. For instance, seams may also be formed in a graft
body section 15 by the use of a fully or partially heated clamshell
mold whose inner surfaces contain raised seam-forming extensions.
These extensions may be configured and preferentially or generally
heated so that when the mold halves are closed over a graft body
section 15 disposed on a mandrel, the extensions apply heat and
pressure to the graft body section directly under the extensions,
thereby "branding" a seam in the graft body section in any pattern
desired and in a single step, saving much time over the technique
described above in conjunction with seam forming apparatus 52.
[0085] If the fusible material comprises ePTFE, it is also possible
to infuse or wick an adhesive (such as FEP or PFA) or other
material into the ePTFE layers such that the material flows into
the fibril/node structure of the ePTFE and occupies the pores
thereof. Curing or drying this adhesive material will mechanically
lock the ePTFE layers together through a continuous or
semi-continuous network of adhesive material now present in and
between the ePTFE layers, effectively bonding the layers
together.
[0086] FIG. 14 illustrates a substantially completed set of seams
81 formed in the layers of fusible material of the graft body
section 15, which seams form inflatable channels 82. FIG. 15
illustrates graft body section 15 as fluid (such as compressed gas)
is injected into the inflation line 36 and in turn into the
inflatable channel network 84 of body section 15, as shown by arrow
84A. The fluid is injected to pre-stress the inflatable channels 82
of body section 15 and expand them outward radially. The fluid may
be delivered or injected through an optional elongate gas
containment means having means for producing a permeability
gradient in the form of a manifold or pressure line 85. The
pressure line 85 shown in FIG. 15 has a configuration with an input
(not shown) located outside the inflation line and a plurality of
outlet apertures or orifices (not shown) that may be configured to
provide an even distribution of pressure within the inflatable
channel network 84. Other fluid injection schemes and
configurations are of course possible.
[0087] Because ePTFE is a porous or semi-permeable material, the
pressure of exerted by injected fluids such as pressurized gas
tends to drop off or diminish with increasing distance away from
the outlet apertures or orifices (not shown) of manifold or
pressure line 85. Therefore, in some embodiments, pressure line 85
may comprise apertures or orifices (not shown) which, when disposed
in graft body section 15, progressively increases in size as one
moves distally along the pressure line towards the proximal end 17
graft body section 15 in order to compensate for a drop in pressure
both within the inflatable channel network 84 and within the
manifold or pressure line 85 itself.
[0088] Once some or all of the inflatable channels 82 have been
pre-expanded or pre-stressed, the graft body section 15 and shape
forming mandrel assembly 89 may then be positioned within an outer
constraint means in the form of a mold to facilitate the inflatable
channel expansion and sintering process. One half of a mold 90
suitable for forming an embodiment of a graft body section 15 such
as that shown in FIG. 15 is illustrated in FIG. 16A. A mold half
body portion 91 is one of two pieces of mold 90. A mold similar to
mold 90 could be made from any number of mold body portions
configured to fit together. For example, a mold 90 could be
designed from three, four, five or more mold body portions
configured to fit together to form a suitable main cavity portion
93 for maintaining the shape of graft body section 15 during
channel expansion and sintering. For certain configurations, a
one-piece mold may be used.
[0089] Mold body portion 91 has a contact surface 92 and a main
cavity portion 93. Main cavity portion 93 has an inside surface
contour configured to match an outside surface contour of the graft
body section with the inflatable channels in an expanded state.
Optional exhaust channels 92A may be formed in contact surface 92
and provide an escape flow path for pressurized gas injected into
the inflatable channel network 84 during expansion of the
inflatable channels 82.
[0090] The main cavity portion 93 of the FIGS. 16A-16B embodiment
is substantially in the shape of a half cylinder with
circumferential channel cavities 94 for forming the various
inflatable channels 82 of graft body section 15. Cavity 93 has a
first tapered portion 95 at the proximal end 96 of mold 90 and a
second tapered portion 97 at the mold distal end 98. FIG. 16B shows
an end view of mold 90 with the two mold body portions 91 and 100
pressed together with the assembly of the graft body section 15 and
shape forming mandrel 14 disposed mold cavity 93.
[0091] FIG. 16C shows the assembly of the graft body section 15 and
shape forming mandrel 14 disposed within mold 90, with the
circumferential inflatable channels 82 of the graft body section 15
aligned with the circumferential channel cavities 94 of the main
cavity portion 93. One mold body portion 100 of mold 90 is not
shown for the purpose of clarity of illustration. A pressurized
fluid indicated as being delivered or injected into manifold or
pressure line 85 by arrow 85A.
[0092] FIG. 17 illustrates by the phantom lines how the outer
layers 94A of circumferential inflatable channel 82 of the fusible
material of a graft body section 15 are expanded into the
circumferential channel cavity 94 of mold cavity 93. The direction
of the expansion of the outer layers 94A to the position indicated
by the phantom lines is indicated by arrow 94B. A cross sectional
view of the seams 83 of the circumferential inflatable channel 82
is shown in FIG. 17 as well.
[0093] While the graft body section network of inflatable channels
84 is in an expanded state by virtue of pressurized material being
delivered or injected into pressure line 85, the entire assembly
may be positioned within an oven or other heating device (not
shown) in order to bring the fusible material of graft body section
15 to a suitable temperature for an appropriate amount of time in
order to fix or sinter the fusible material. In one embodiment, the
fusible material is ePTFE and the sintering process is carried out
by bringing the fusible material to a temperature of between about
335 and about 380 degrees Celsius; specifically, between about 350
and about 370 degrees Celsius. The mold may then be cooled and
optionally quenched until the temperature of the mold drops to
about 250 degrees Celsius. The mold may optionally further be
quenched (for handling reasons) with ambient temperature fluid such
as water. Thereafter, the two halves 91 and 100 of mold 90 can be
pulled apart, and the graft assembly removed.
[0094] The use of mold 90 to facilitate the inflatable channel
expansion and sintering process is unique in that the mold cavity
portion 93 acts as a backstop to the graft body section so that
during sintering, the pressure created by the injected fluid that
tends to expand the inflatable channels outward is countered by the
restricting pressure exerted by the physical barrier of the
surfaces defining the mold cavity 93. In general terms, therefore,
it is the pressure differential across the inflatable channel ePTFE
layers that in part defines the degree of expansion of the channels
during sintering. During the sintering step, the external pressure
exerted by the mold cavity surface competes with the fluid pressure
internal to the inflatable channels (kept at a level to counteract
any leakage of fluid through the ePTFE pores at sintering
temperatures) to provide an optimal pressure differential across
the ePTFE membrane(s) to limit and define the shape and size of the
inflatable channels.
[0095] Based on this concept, we have found it possible to use
alternatives to a mold in facilitating the inflatable channel
expansion process. For instance, it is possible inject the channel
network with a working fluid that does not leak through the ePTFE
pores and to then expand the network during sintering in a
controlled manner, without any external constraint. An ideal fluid
would be one that could be used within the desired ePTFE sintering
temperature range to create the necessary pressure differential
across the inflatable channel membrane and the ambient air, vacuum,
or partial vacuum environment so to control the degree of expansion
of the channels. Ideal fluids are those that possess a high boiling
point and lower vapor pressure and that do not react with ePTFE,
such as mercury or sodium potassium. In contrast, the network of
inflatable channels 84 can also be expanded during the fixation
process or sintering process by use of vapor pressure from a fluid
disposed within the network of inflatable channels 84 For example,
the network of inflatable channels 84 can be filled with water or a
similar fluid prior to positioning assembly in the oven, as
discussed above. As the temperature of the graft body section 15
and network of inflatable channels 84 begins to heat, the water
within the network of inflatable channels 84 begins to heat and
eventually boil. The vapor pressure from the boiling water within
the network of inflatable channels 84 will expand the network of
inflatable channels 84 provided the vapor is blocked at the
inflation line 85 or otherwise prevented from escaping the network
of inflatable channels.
[0096] FIG. 18 shows an elevational view in partial longitudinal
section of an endovascular graft assembly 105 manufactured by the
methods and with the apparatus described above. Endovascular graft
assembly 105 comprises a graft body section 108 with a proximal end
106, a distal end 107, and circumferentially oriented inflatable
channels 111 shown in an expanded state. A longitudinal inflatable
channel 116 fluidly communicates with the circumferential
inflatable channels 111.
[0097] An expandable member in the form of a proximal connector
member 112 is shown embedded between proximal end wrap layers 113
of fusible material. An expandable-member in the form of a distal
connector member 114 is likewise shown embedded between distal end
wrap layers 115 of fusible material. The proximal connector member
112 and distal connector member 114 of this embodiment are
configured to be secured or connected to other expandable members
which may include stents or the like, which are not shown. In the
embodiment of FIG. 18, such a connection may be accomplished via
connector elements 117 of the proximal and distal connector members
112 and 114, which extend longitudinally outside of the proximal
and distal end wrap layers 113 and 115 away from the graft body
section 108.
[0098] The FIG. 18 embodiment of the present invention features
junction 118 between the distal end wrap layers 115 of fusible
material and the layers of fusible material of a distal end 121 of
the graft assembly main body portion 122. There is likewise a
junction 123 between the proximal end wrap layers 113 and the
layers of fusible material of a proximal end 124 of the graft
assembly main body portion 122. The junctions 118 and 123 may be
tapered, with overlapping portions that are bound by sintering or
thermomechanical compaction of the end wrap layers 113 and 115 and
layers of the main body portion 122. This junction 123 is shown in
more detail in FIG. 19.
[0099] In FIG. 19, six proximal end wrap fusible material layers
113 are disposed between three fusible material inner layers 125
and three fusible material outer layers 126 of the main body
portion proximal end 124.
[0100] FIG. 20 illustrates a sectional view of a portion of the
distal connector member 114 disposed within the distal end wrap
layers 115 of fusible material. Connector member 114 is disposed
between three outer layers 127 of fusible material and three inner
layers 128 of fusible material. Optional seams 127A, formed by the
methods discussed above, are disposed on either side of distal
connector member 114 and mechanically capture the connector member
114. FIG. 21 likewise is a transverse cross sectional view of the
proximal connector member 112 embedded in the proximal end wrap
layers 113 of fusible material.
[0101] FIG. 22 illustrates a transverse cross section of the
longitudinal inflatable channel 116 formed between main body
portion 122 outer layers 131 and the main body portion 122 inner
layers 132. FIG. 23 is a transverse cross section of graft main
body portion 122 showing a circumferential inflatable channel 111
in fluid communication with longitudinal inflatable channel 116.
The circumferential inflatable channel 111 is formed between the
outer layers 131 of fusible material of main body portion 122 and
inner layers 132 of fusible material of main body portion 122.
[0102] While particular forms of embodiments of the invention have
been illustrated and described, it will be apparent that various
modifications can be made without departing from the spirit and
scope of the invention. Accordingly, it is not intended that the
invention be limited, except as by the appended claims.
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